In previous electrical communications systems, electrical switches were used to route the signals throughout the system by redirecting the signals from various input ports to various output ports. More recently, fiber optics communications networks have been used for added bandwidth. Typically, in these fiber optic networks, the signals are transmitted as light though optical fibers, but the redirection of the signals is still performed with electrical switches. That is, photons of the light beams are converted to an intermediary medium (such as transduction to an electrical charge or voltage) during the switching process.
There are, however, various proposals for using all optical switches. These optical switches are adapted for using a reflective surface to redirect in incident light beam in one or more directions. For instance, European Patent Application EP 0 936 066 A1 describes using micromachined mechanically actuated mirrors to steer the light beams. In another type of optical switch, for example, as disclosed in U.S. Pat. No. 5,699,462, ink jet technology is used to create bubbles actuated in a liquid medium to reroute the signals. And European Patent No. EP 0 550 022 B1 describes an optical switch which uses an electrostatically actuated flexible reflective membrane to steer the light beam in other directions.
The present invention implements a fluidic all-optical switch that alters the path of a light beam by controlling the geometry of a reflective surface which is defined by the interface between two fluids.
In one aspect of the invention, the optical switch includes a first fluid, and a second fluid positioned adjacent to and in contact with the first fluid. The interface between the first fluid and the second fluid defines a reflective surface that provides total internal reflectance (TIR) for a range of incident angles. The optical switch also includes electrodes for applying an electrical field across the second fluid to alter the geometry of the reflective surface and redirect an incident light beam in one or more directions.
Embodiments of this aspect may include one or more of the following features. The first fluid is a conductive fluid, and the second fluid is an insulating fluid. The first fluid can be a liquid and the second fluid can be a gas. In another embodiment, the first and second fluids can be two immiscible liquids. The first or second fluid can be an organic liquid.
In particular embodiments of this aspect, the first fluid is biased with a constant voltage, and the electrical field which actuates the reflective surface is generated by varying the voltage potential across the second fluid. The varying voltage potential can be created by energizing one or more electrodes positioned on the same side of the reflective surface as the second fluid. The variable voltage can be modulated so that the incident light beam is redirected with little resonance.
In certain embodiments, the optical switch includes a well in which the second fluid resides, and the electrodes are positioned at the bottom of the well. The well can have a depth of about 0.001 to 0.01 inch and a diameter of about 0.02 to 0.07 inch. In one embodiment, the well has a depth of about 0.01 inch and a diameter of about 0.06 inch.
In some embodiments, the fluid interface is formed within an aperture or orifice of a ring positioned over the well. Alternatively, the optical switch can be provided with two layered rings. The combination of the two rings has a inner rim which defines an orifice such that the reflective surface attaches to the rim where the two rings meet. In some arrangements, each ring has a diameter of about 0.02 to 0.07 inch, and a thickness of about 0.00004 to 0.003 inch, in which case the well has a diameter of about 0.1 inch. The first ring can be made of hydrophilic material which attracts liquid, while the second ring can be made from a hydrophobic material which repels liquids. The first ring can also be made from hydrophobic material, and the second ring can be made from hydrophillic material.
The aperture or orifice positioned over the well can be circular or non-circular in shape. The shape and size of the orifice can be varied to alter the natural frequency of the reflective surface. The natural frequency of the optical switch can also be varied by altering the size of the well and the density of the first and second fluids.
The well is typically formed by etching a silicon substrate, and the electrodes are usually embedded in or formed on the substrate.
The optical switch can also include a transparent housing which contains the first fluid. The housing can be made from, for example, acrylic. A wall of the transparent housing is usually oriented so that the incident light beam is orthogonal to the wall. In this configuration, the switch can be used for laser alignment and steering. The optical switch can also include a housing which contains the first fluid and serves to align input and output optical fibers or waveguides.
The optical switch is able to redirect an incident light beam between two points within a very short period of time (e.g., less than about 1 msec). The optical switch is also able to redirect an incident light beam from one or more incoming directions to a multiplicity of directions. For instance, the optical switch can operate as a 1-to-N switching element, where there are N discrete targets. Also, the device is analog in nature, thus the output beam can be steered in a continuous manner.
Related aspects of the invention include a method of steering an incident light beam. The method includes providing a reflective surface defined at the interface between a first fluid and a second fluid, and actuating the reflective surface to alter the geometry of the reflective surface, thereby redirecting the direction of an incident light beam that strikes the reflective surface.
Among other advantages, the optical switch is capable of redirecting an incident light beam in very short time periods, for instance, in under one msec. The optical switch is a pure photonic switch; that is there are no transductions between the input and. the output side of the switch. The all-optically switch does not rely on micro-mechanical structures, mirrors, or other devices that might reduce reliability and degrade performance. The switch is suitable for many different applications. For instance, the switch operates in some applications as a 1-to-N switching interface with a single input switching to a plurality of outputs. In other applications, the optical switch is implemented as an M-to-N switching interface, where M is greater than one. Further, the reflective surface is actuated with electrostatic forces which requires no electrical current. In addition, the switch can be activated to maintain a constant light displacement for prolonged periods of time with a small electrostatic voltage. There are particular advantages of using a fluid-fluid interface as the reflective surface. For instance, the reflective surface provides total internal reflectance, that is, nearly 100% reflectance. The optical switch is simple to construct and assemble, thereby minimizing the costs to fabricate the switch. The reflective surface is under uniform tension, and provides a more uniform surface than micromachined surfaces.
Still further aspects, features, and advantages follow.